Some Tips In Object C

源自：http://blog.csdn.net/kmyhy/archive/2010/07/06/5716755.aspx

1.使用class获得meta class

NSLog (@"Class name : %@",[[[arr objectAtIndex:i] class] description]);

2.使用NSClassFromString和 NSSelectorFromString

id object = [[ NSClassFromString (@ "NameofClass" ) alloc ] init ];// NSClassFromString加载的类不需要import SEL sel　=　NSSelectorFromString(@"doSomethingMethod:")//注意这个冒号,说明方法带有参数

if ([object　respondsToSelector:sel]) {

[object　performSelector:sel　withObject:color]; //注意如果有两个参数,使用两个withObject:参数;

}

3.使用isa

id movie=[arrFavorite objectAtIndex :row];

if (movie->isa ==[IndexPageItem class ]) {

NSLog ( @"movie title:%@",[movie description ]);

}

4.谓词

NSArray * arr=[ NSArray arrayWithObjects : @"1", @"0", @"no", @"NO", @"YES", @"yes", nil ];

NSPredicate* predicate=[ NSPredicate predicateWithFormat :

@"SELF IN{'0','no','NO'}"];

NSArray * result=[arr filteredArrayUsingPredicate :predicate];

NSLog (@"%@" ,result);

for (NSString * s in arr){

NSLog( @"%@:%d" ,s,[predicate evaluateWithObject:s]);

}

5. From NSString to NSData

NSString * text = @ "Some string" ;

NSData * data = [ text dataUsingEncoding: NSUTF8StringEncoding] ;

6. From NSData to NSString

NSString * text = [ [ NSString alloc] initWithData: data encoding: NSUTF8StringEncoding] ;

7.日期和时间

NSCalendar * gregorian = [[ NSCalendar alloc ] initWithCalendarIdentifier : NSGregorianCalendar ];

NSDateComponents * todayComponents = [ gregorian components :( NSDayCalendarUnit | NSMonthCalendarUnit | NSYearCalendarUnit ) yourDate ];

NSInteger theDay = [ todayComponents day ];

NSInteger theMonth = [ todayComponents month ];

NSInteger theYear = [ todayComponents year ];

// now build a NSDate object for yourDate using these components

NSDateComponents * components = [[ NSDateComponents alloc ] init ];

[ components setDay : theDay ];

[ components setMonth : theMonth ];

[ components setYear : theYear ];

NSDate * thisDate = [ gregorian dateFromComponents : components ];

[ components release ];

// now build a NSDate object for the next day

NSDateComponents * offsetComponents = [[ NSDateComponents alloc ] init ];

[ offsetComponents setDay : 1 ];

NSDate * nextDate = [ gregorian dateByAddingComponents : offsetComponents toDate : yourDate options : 0 ];

[ offsetComponents release ];

[ gregorian release ];

8.使用 performSelectorInBackground（多线程）调用的方法，必须 在该方法中 用 NSAutoreleasePool

否则出现错误： no pool in place - just leaking。如果用performSelector则没有这个问题。

9.ld: symbol(s) not found 错误的解决办法

展开"Targets-->Compile Sources"，查看列出的所有.m文件，找出其中缺失的.m文件，拖到其中。

10.Ojbect C让线程休眠

[ NSThread sleepForTimeInterval: 2 ];//单位是秒

11.nil和NULL的区别

在Object C中，NULL和nil都是空指针，不同的是，NULL用于c 指针，即（void *）；而nil用于c++或java对象，即id为空

12.字符串替换

str=[str stringByReplacingOccurrencesOfString: @"[]" withString: @"" ];

13.assign，copy，retain之间的区别

assign ： 简单赋值，不更改索引计数（Reference Counting）。

copy ： 建立一个索引计数为1的对象，然后释放旧对象

retain ：释放旧的对象，将旧对象的值赋予输入对象，再提高输入对象的索引计数为1

retain的实际语法为：

- ( void ) setName: ( NSString * ) newName {

if ( name != newName) {

[ name release] ;

name = [ newName retain] ;

// name’s retain count has been bumped up by 1

}

}

说了那么麻烦，其实接下来的话最重要：

?如果你不懂怎么使用他们，那么就这样 ->

使用assign: 对基础数据类型 （NSInteger，CGFloat）和C数据类型（int, float, double, char, 等等）

使用copy： 对NSString

使用retain： 对其他NSObject和其子类

14.nonatomic关键字：

atomic是Objc使用的一种线程保护技术，基本上来讲，是防止在写未完成的时候被另外一个线程读取，造成数据错误。而这种机制是耗费系统资源的，所以在iPhone这种小型设备上，如果没有使用多线程间的通讯编程，那么nonatomic是一个非常好的选择。

15.发送短信／邮件／打电话

+ (void)alert:(NSString *)msg
{
UIAlertView *alertView = [[[UIAlertView alloc] initWithTitle:msg message:@"" delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil, nil] autorelease];
[alertView showWithBackground];
}

+ (NSString*) cleanPhoneNumber:(NSString*)phoneNumber
{
NSString* number = [NSString stringWithString:phoneNumber];
NSString* number1 = [[[number stringByReplacingOccurrencesOfString:@" " withString:@""]
// stringByReplacingOccurrencesOfString:@"-" withString:@""]
stringByReplacingOccurrencesOfString:@"(" withString:@""]
stringByReplacingOccurrencesOfString:@")" withString:@""];

return number1;
}

+ (void) makeCall:(NSString *)phoneNumber
{
if ([DeviceDetection isIPodTouch]){
[UIUtils alert:kCallNotSupportOnIPod];
return;
}

NSString* numberAfterClear = [UIUtils cleanPhoneNumber:phoneNumber];

NSURL *phoneNumberURL = [NSURL URLWithString:[NSString stringWithFormat:@"tel:%@", numberAfterClear]];
NSLog(@"make call, URL=%@", phoneNumberURL);

[[UIApplication sharedApplication] openURL:phoneNumberURL];
}

+ (void) sendSms:(NSString *)phoneNumber
{
if ([DeviceDetection isIPodTouch]){
[UIUtils alert:kSmsNotSupportOnIPod];
return;
}

NSString* numberAfterClear = [UIUtils cleanPhoneNumber:phoneNumber];

NSURL *phoneNumberURL = [NSURL URLWithString:[NSString stringWithFormat:@"sms:%@", numberAfterClear]];
NSLog(@"send sms, URL=%@", phoneNumberURL);
[[UIApplication sharedApplication] openURL:phoneNumberURL];
}

+ (void) sendEmail:(NSString *)phoneNumber
{
NSURL *phoneNumberURL = [NSURL URLWithString:[NSString stringWithFormat:@"mailto:%@", phoneNumber]];
NSLog(@"send sms, URL=%@", phoneNumberURL);
[[UIApplication sharedApplication] openURL:phoneNumberURL];
}

+ (void) sendEmail:(NSString *)to cc:(NSString*)cc subject:(NSString*)subject body:(NSString*)body
{
NSString* str = [NSString stringWithFormat:@"mailto:%@?cc=%@&subject=%@&body=%@",
to, cc, subject, body];

str = [str stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

[[UIApplication sharedApplication] openURL:[NSURL URLWithString:str]];

}
16.将 NSString 转换编码 集 为 gb2312
NSURL * url = [ NSURL URLWithString : urlStr] ;
NSData * data = [ NSData dataWithContentsOfURL : url ] ; NSStringEncoding enc = CFStringConvertEncodingToNSStringEncoding( kCFStringEncodingGB_18030_2000) ; NSString * retStr = [ [ NSString alloc ] initWithData : data encoding : enc] ;

17.将指定格式的字符串转换为日期类型
//把 yyyyMMddHHmmss格式的字符串转换为 NSDate类型
-(NSDate *)stringToDate:(NSString *)dateString{
NSDateFormatter *dateFormatter = [[ NSDateFormatter alloc ] init ];
[dateFormatter setDateFormat :@"yyyyMMddHHmmss" ];
NSDate *date = [dateFormatter dateFromString :dateString];
[dateFormatter release ];
return date; }
18." Array was mutated while being enumerated"问题的解决
在操作数组对象时进行同步，如：

@synchronized(enemiesArray) {

⋯⋯

数组操作代码

⋯⋯

}
19、字符串与数组之间的转换： SString *string=@"one:two:three:four"; NSArray *result=[string componentsSeparatedByString:@":"]; string=[result componentsJoinedByString:@"_"]; 20、定时器NSTimer//1秒后，触发定时器事件

NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self

selector:@selector(timerFired) userInfo:nil repeats:NO];
21、让UITextField里面的text垂直居中可以这样写:

text.contentVerticalAlignment = UIControlContentVerticalAlignmentCenter;
22、在UITextField最右侧加图片是以下代码,

UIImageView *imgv=[[UIImageView alloc] initWithImage:[UIImage imageNamed:@"right.png"]];

text.rightView=imgv;

text.rightViewMode = UITextFieldViewModeAlways;

如果是在最左侧加图片就换成:

text.leftView=imgv;

text.leftViewMode = UITextFieldViewModeAlways;